28-1 Worksheet Questions

How many components to image quality?

5

During a 360 degree x ray tube rotation the couch moves 8mm. Beam collimation is 5mm what's the pitch?

8/5= 1.6:1 is the pitch

Radiation Flux

A measure of the amount of radiation received by an object from a given source

Which of the following CT Pitch values results in overlapping images: A.) 0.5:1 B.) 1.0:1 C.) 2.0:1 D.) 10.0:1

A.) 0.5:1

Which of the following refers to the ability of the computer tomography detector to caputer, absorb, and convert x ray photons into electrical engergy: A.) efficiency B.) stability C.) response time D.) dynamic range

A.) efficiency

Heterogeneous Beam

Attenuation is not exponential but rather both the quantity and quality of the photons change As a result, the penetrating power of the photons increases and the beam becomes harder

Larger pixel size actually increases spatial resolution due to more information being detected: A.) True B.) False

B.) False

Thicker slice thickness allows for better spatial resolution because more tissue volume can be used to create the image. A.) True B.) False

B.) False

How accurately a system displays the image when compared to the actual object is: A.) DQE B.) MTF C.) DAS D.) ADC

B.) MTF

________ is responsible for converting contrast values of objects (subject contrast) into contrast intensity levels in the image (image contrast). A.) DQE B.) MTF C.) DAS D.) ADC

B.) MTF

Electromechanical devices made up of rings and brushes to transmit electrical energy across a rotating interface are called: A.) Target Rings B.) Slip Rings C.) Helical Rings D.) Spiral Rings

B.) Slip Rings

Hounsfield scale

Based on attenuation of water as a reference point Water= 0 HU Bone= +1000 HU Air= -1000 HU

Pitch formula

Beam width x seconds x pitch = amount of tissue --------------------------------------------------------- Gantry rotation time 8mm x 25s x 1.5/2s of gantry rotation time = amount of tissue.

data acquisition

Conversion of electrical signals obtained form the electronic detectors. The image of whatever the CT scanner see's that will be sent to a computer for image reconstruction

Formation of CT images but CT scanner involves what three steps

Data acquisition (Machine taking the image) Image reconstruction (Computer converting the data from the machine into an image) Image display (Simply the monitor that the image is viewed on)

Image quality Contrast resolution

Differentiating resolution

Contrast resolution

Distinguish between parts of body

Image quality Radiation dose

Enough photons striking the detector

Electromagnetic deflection coils

Fifth Generation

Electron Beam scanning

Fifth Generation

Pencil Beam

First Generation

Single detector translate - rotate

First Generation

Ring of stationary detectors

Fourth Generation

Slip-Ring Technology

In a slip-ring gantry system, power and electrical signals are transmitted through stationary rings within the gantry Eliminating the need for electrical cables

Helical Technology

Introduced in 1990•Allowed continuous rotation Power and signals transmitted to rotating gantry using brushes on static rings No need to start and stop rotation Scan times as fast as 0.3 s

What is Volume Data Acquisition?

May be referred to as spiral or helical scanning Used to scan a volume of tissue rather than one slice at a time Single-slice CT (SSCT) Multislice CT (MSCT)

Image quality Artifact

Necklace on or other things still one

Image quality Spatial resolution

Pixels

First use of Bow tie filter

Second Generation

First use of more than one detector

Second Generation

What two methods for Data Acquisition?

Slice-by-slice data acquisition Volume data acquisition

Image quality Image noise

Static

The Tomographic Principle

The larger the tomographic angle the thinner the tomographic section

Homogenous Beam

The quality of the beam, or beam energy, does not change as it is attenuated

What is Slice-by-Slice Acquisition?

The x-ray tube rotates around the patient and collects data for the first slice The tube stops, and the patient moves into position for the next slice The process is repeated until all slices are acquired "Step and Shoot"

Image manipulation

Think of it as snapchat filters, it manipulates gray-scale, edge enhancement, 3D processing etc Transverse image can be reformatted into coronal, sagittal and paraxial sections. Another form of image manipulation

Helical scanning

Third Generation

Ring artifact

Third Generation

Slip ring

Third Generation

step and shoot

Third Generation

Windowing means

Windowing, also known as grey-level mapping, contrast stretching, histogram modification or contrast enhancement The process in which the CT image greyscale component of an image is manipulated via the CT numbers doing this will change the appearance of the picture to highlight particular structures. The brightness of the image is adjusted via the window level. The contrast is adjusted via the window width.

In its simplest configuration, the CT imaging system consists of an x-ray source and which of the following? a.) A detector. b.) A selenium plate. c.) A video display terminal. d.) An image intensifier. e.) An x-ray beam collimator.

a.) A detector.

Which of the following is characteristic of first generation CT imaging systems? a.) A pencil x-ray beam. b.) A selenium or film image receptor. c.) Multiple sources and multiple detectors. d.) Rotate-only geometry. e.) Slip rings.

a.) A pencil x-ray beam.

Fourth-generation CT imaging systems: a.) Are faster than third-generation CT imaging systems. b.) Have rotate-rotate geometry. c.) Incorporate area-beam geometry. d.) May use Selenium or film as the image receptor. e.) Require prepatient collimation.

a.) Are faster than third-generation CT imaging systems.

A CT imaging system produces which type of image? a.) Axial b.) Biaxial c.) Fulcrum plane d.) Longitudinal e.) Transverse

a.) Axial

Which of the following has been used as a detector in a CT imaging system? a.) Bismuth germanate. b.) CaWO4 c.) High-pressure air. d.) Selenium. e.) Silver Halide

a.) Bismuth Germanate

Second-generation CT imaging systems: a.) Have a multiple detector array. b.) Have rotate-rotate geometry. c.) Require imaging speeds from 1 to 5 minutes. d.) Require special patient preparation. e.) Use increments of 1 degree per view.

a.) Have a multiple detector array.

The translate-rotate mode: a.) Collects data only during the rotate portion. b.) Describes both first and second generation CT imaging systems. c.) Requires higher heat capacity x-ray tubes. d.) Requires only solid-state detectors. e.) Results in imaging times as short as 1 s.

b.) Describes both first and second generation CT imaging systems.

Noise on a CT image can be reduced by: a.) Increasing kVp. b.) Increasing mAs. c.) Increasing matrix size. d.) Reducing image size. e.) Reducing pixel size.

b.) Increasing mAs.

Sensitivity profile in CT is determined principally by the: a.) Bow-tie filter. b.) Predetector collimator. c.) Prepatient collimator. d.) Reconstruction algorithm. e.) Ramp function.

b.) Predetector collimator.

Third-generation CT imaging systems have which of the following? a.) Multiple-detector, area-beam geometry. b.) Rotate-rotate geometry. c.) Rotate-translate geometry. d.) Single-detector, fan-beam geometry. e.) Translate-translate geometry.

b.) Rotate-rotate geometry.

Each translation of a source detector assembly produces which of the following? a.) A matrix. b.) A pixel. c.) A projection. d.) A voxel. e.) An image.

c.) A projection.

CT mA is modulated to: a.) Improve image contrast. b.) Minimize beam hardening. c.) Reduce patient dose. d.) Reduce scatter radiation. e.) Reduce x-ray tube loading.

c.) Reduce patient dose.

Which of the following subsystems would normally be associated with the gantry assembly? a.) Image postprocessing. b.) The algorithms. c.) The detector array. d.) The physician's viewing console. e.) The software.

c.) The detector array.

Spatial resolution for CT imaging systems is approximately: a.) 1 cm. b.) 10 cm. c.) 100 mm. d.) 1 mm. e.) 10 mm.

d.) 1 mm.

In a CT imaging system, prepatient collimation: a.) Controls pixel size. b.) Controls scatter radiation that reaches the detector. c.) Determines image noise. d.) Determines patient dose. e.) Determines slice thickness.

d.) Determines patient dose.

The thickness of section in CT depends primarily on: a.) kVp b.) mAs c.) Matrix size d.) Predetector collimation e.) Prepatient collimation

d.) Predetector collimation

Slice thickness can also be expressed as which of the following? a.) Dose profile. b.) Low-contrast profile. c.) Resolution profile. d.) Sensitivity profile. e.) Spatial profile.

d.) Sensitivity profile.

DQE

detective quantum efficiency - High DQE indicates that less radiation is needed to achieve identical image.

CT imaging systems incorporate: a.) Charged electrostatic plates. b.) High-frequency radiographic grids. c.) Light-localizing, variable-aperture collimators. d.) Automatic brightness control. e.) A gantry.

e.) A gantry.

A comparison of scintillation and gas-filled detectors shows that: a.) Both have approximately the same total detection efficiency. b.) Both rely heavily on Compton interaction c.) Only scintillation detectors require prepatient collimation. d.) The gas-filled detectors have higher intrinsic efficiency. e.) The scintillation detectors have higher geometric efficiency.

e.) The scintillation detectors have higher geometric efficiency.

Window level:

the center of the range The window level (WL), often also referred to as window center, is the midpoint of the range of the CT numbers displayed.

Window width:

the range of CT numbers The window width (WW) as the name suggests is the measure of the range of CT numbers that an image contains. A wider window width (2000 HU will display a wider range of CT numbers. Consequently, the transition of dark to light structures will occur over a larger transition area to that of a narrow window width (<1000 HU)